O chá está quente.

Because chá is a masculine noun in Portuguese. Portuguese nouns have grammatical gender, so they normally go with either o or a in the singular.

A useful habit is to learn new nouns together with their article:

• o chá
• a água
• o café

This gender is grammatical, not biological.

Chá is pronounced roughly like shah in English.

A couple of important points:

• ch in Portuguese usually sounds like English sh
• the accent mark in chá shows the stressed vowel
• it is one syllable

Portuguese usually uses estar for temporary states or conditions, and ser for identity, definition, or more permanent characteristics.

Temperature is normally treated as a temporary condition, so:

• O chá está quente = the tea is hot

If you said O chá é quente, it would sound more like a general statement about tea, not the condition of this tea right now.

The accent shows where the stress goes: es-TÁ.

It also helps distinguish está from esta:

• está = is
• esta = this, feminine

So the accent is important both for pronunciation and meaning.

In Brazilian Portuguese, quente is roughly KEN-chee in many accents, though the first vowel is actually nasal, so the English approximation is not perfect.

A few pronunciation notes:

• qu before e sounds like k
• the first syllable has a nasal vowel
• the final e in Brazilian Portuguese often sounds like ee
• in some regions, the t stays more like a clear t, so you may hear something closer to KEN-tee

It can mean either hot or warm, depending on context.

For example:

• O chá está quente could mean the tea is pleasantly hot or just warmish-hot
• if you want to make it stronger, you can say muito quente = very hot

So quente covers a range that English sometimes splits into warm and hot.

Some Portuguese adjectives have the same form for both genders in the singular, and quente is one of them.

So you get:

• o chá está quente
• a sopa está quente

But the plural does change:

• os chás estão quentes
• as sopas estão quentes

Because this sentence follows the common pattern:

subject + form of estar + adjective

So:

• O chá = subject
• está = is
• quente = hot

This is the normal way to say The tea is hot.

They are related, but they are not the same structure.

• chá quente = hot tea
  This is a noun phrase.
• O chá está quente = The tea is hot
  This is a full sentence.

So chá quente names a kind of tea or describes the tea directly, while O chá está quente makes a complete statement.

Normally, no. In a full sentence like this, Portuguese usually wants the article with a specific singular noun, so O chá está quente sounds natural.

Without the article, Chá está quente sounds incomplete or unnatural in ordinary speech.

Yes. Tá is a very common spoken short form of está in Brazilian Portuguese.

So in everyday conversation, you will often hear:

• O chá tá quente

In careful writing or more formal speech, está is the standard form.